Antenna structure



Nov. 18, 1941. F. GERTH ETAL v 2,263,460

ANTENNA STRUCTURE Filed Jan. 9, 193e 14H02' @y l Patented Nov. 18, 1941ANTENNA STRUCTURE Felix Gerth, Berlin-Tempelhof, and Walter MaxHahnemann, Berlin-Marienfelde, Germany, assignors to C. LorenzAktiengesellschaft, Berlin- Tempelhof, Germany, a company ApplicationJanuary 9, 1936, Serial No. 58,314 In GermanyJanuary 12, 1935 (Cl.Z50-33) 1 Claim.

In order to prevent disturbing fields from occurring in the operation ofantenna structures intended for broadcasting arrangements as provided bythe invention have a self-oscillating mast, that extends to the earthssurface and is excited at its lower end while operating as a dipolewhich has capacity surfaces at its upper and lower ends and whose centreof oscillation is a quarter of a wavelength, or nearly so, above theearths surface.

It is well known per se to employ oscillation masts, namely in the formknown as Blau-Knoxantennas. Such an antenna consists in an upright mastextending substantially to the earths surface but insulated from theearth and tuned to the operative wavelength while being excited at itslower end. In order to ensure that the current distribution isadvantageous as regards the diagram of radiation, the mast height in thecase of the Blau-KnoX-antenna is about 0.6 i, if i is the operativewavelength. The method of exciting a mast as a dipole fed at its lowerend has the advantage that the mast height may be much less than inother cases. In general a height equal to 0.4 A will be sufficient. Thisis advantageous not only from an economical point of view but isdesirable also for the reason that high masts endanger air trame. Theuse of self-oscillating masts has the advantage above all that thearrangement is much cheaper than the prior ones, since iron masts areknown to be much cheaper than wooden masts and cheaper also than mastscomprising wooden and iron members, a construction that might beaccomplished by making the lower part of iron and the upper of wood.

The invention is explained hereafter by way of example. Figs. l, 2, 3and 4 are diagrammatic elevations showing each one embodiment of theinvention, Fig. 4 being in the nature of a partial reproduction of Fig.l.

In the arrangement according to Fig. 1 the oscillating mast I is not initself proof against breaking down and is therefore attached to theground by span ropes 2, 3, 4 arranged around the mast in the usualmanner. The ropes are subdivided at suitable points by insulators I6 ina manner well known per se. The ropes 2, 4 are arranged also to formcapacity surfaces at the two ends of the dipole constituted by the mast.To such end they have bronze parts I1 by which they are attached to themast. These parts I1 are represented by heavy lines. In order to formthe desired capacity surfaces the ybronze parts I1 are connected to eachother by conduc- 55 tors 5, 6. In the simplest case the rope parts l1are attached to the mast directly. This mode however has thedisadvantage that a subsequent tuning of the mast is not possible. Theinitial design of the mast should be such that the dimensions of themast are inherently tuned to the desired wavelength. It is advantageoushowever to provide for a subsequent slight tuning. This in the caserepresented is accomplished by the conductors 5, 6 not beingconductively connected to the mast directly but through tuning coils 1,8. The tuning may be effected by varying these coils, but may beperformed also by varying the number of bronze parts I1 attached to themast and thus increasing or decreasing the capacity surface. This modehowever has the disadvantage that the radiation diagram will be somewhatunsymmetrical. I8 denotes the transmission line from which the dipole isfed over a coupling device I9.

The mast shown in Fig. 2 is in itself proof against breaking down and istherefore only at its middle attached to the ground by span ropes I0.Ropes II are arranged to form an upper capacity surface, these ropeshaving bronze parts I'I at the top of the mast. A lower capacity surfaceis formed of bronze ropes I 2 which are connected with the ropes I0.

Such ropes I2 may be provided also in the case of arrangements of thekind shown in Fig. l, as will appear from Fig. 4, and here present theadvantage that the lower capacity surface is more remote from the earthsurface, thus causing the current loop to be at a higher level thanotherwise.

As shown in Fig. 3, it is possible also to effect the fine tuning bymeans of a self-induction coil I4 arranged to bridge over an insulationI3 disposed in the middle of the mast I and connected to it electricallyso as to prolong the dipole.

It is advantageous to bridge over the joints of the superposed parts ofthe mast by well conducting means. The simplest mode of performing thisconsists in stretching wires I5 along the mast and fixing them at anumber of points to the longitudinal edges of the mast. Such arrangementis of a special simplicity if the mast is of the same cross-sectionalarea throughout, because in such case it is sufcient to stretch thewires I5 from one end of the mast to the other end thereof.

What is claimed is:

A broadcast antenna structure comprising a continuous conducting mastextending upward from the surface of the earth to a height of abouttwo-fifths of a Wavelength at the frequency to be radiated, a pluralityof tension members having insulated conductive portions for staying saidmast, a plurality of said portions of said tension members beingdisposed to form an extended capacity surface adjacent an upper point ofsaid mast and a further plurality of said portions of said tensionmembers being disposed to form a second capacity surface adjacent anintermediate point of said mast remote from the surface of the earth,means for connecting each of said capacity surfaces to the adjacentpoint of the mast whereby the portion of the mast between said pointsconstitutes a dipole connected at each end to a capacity surface, meansfor eX- citing said dipole at its lower end at the frequency to beradiated, the dimensions of said portion and said surfaces having suchValues that the natural resonance frequency of said di'- pole andcapacity surfaces is inherently approximately equal to the frequency tobe radiated, and the heights of said capacity surfaces above the surfaceof the earth being such that the center of oscillation of said dipole isapprox imately a quarter wavelength above the earth at said frequency,whereby the current distribution produces an advantageous radiationpattern with said total mast height of only about two-fifths of awavelength, and a variable impedance included in at least one of saidmeans for connecting vsaid capacity surfaces to the mast whereby thenatural resonance frequency of said 15 dipole may be slightly varied.

FELIX GERTH. WALTER MAX HAHNEMANN.

